Most of the roller conveyors presently being manufactured utilize shafts or axles with hexagonal cross-sections to mount the rollers between support frames. Each roller is supplied with a pair of bearing assemblies, one for each end which have a complimentary bore for the axle. Similarly, the support structures have openings with identical sections. The primary purpose for the polygonal cross-sections is to prevent the rotation of the inner cone of the bearing assembly about which the spherical elements of the assembly are disposed.
The cost of producing polygonal axles is high due to both the cost of material and the shape of the axle. Attempts have been made to replace the single axle per roller with a pair of short stub axles, one for each end of a roller. From a cost standpoint, the use of such shorter axles to reduce the amount of material used is economical. There are, however, severe functional disadvantages which must be weighed against the beneficial economics. Perhaps the most critical disadvantage is the inability of the prior art stub axles to perform properly under increasingly heavy loads or when there is slight misalignment of the support frame structure.
It has been noted that stub axles under such circumstances tend to cause a distortion or tilting of the inner cone relative to the bearings. This distortion causes the cone to press directly against the balls of the bearing, which ordinarily is separated by a thin film of friction-reducing lubricant, and greatly increasing frictional problems. While most bearings tolerate a certain amount of tilting, for example, about one degree relative to the vertical, the tilting due to misaligned frames or axle deflection due to heavy loads would exceed this amount were it not for the loose fit of the single axle in the support frame structure openings and bore of the bearing assembly.
Because a stub axle is positioned only by one frame, and therefore fixed at a single point, it is necessary that the axle be secured firmly to the frame with its axis perpendicular to the frame. Otherwise, the axle would always pivot downwardly even under the weight of an unloaded roller. Thus, the loose fit needed to compensate for misalignment and/or deflection cannot be provided by the stub axle. This means that the use of stub axles are presently limited to special situations where the loads are extremely light and frame alignment is carefully assured.
Therefore, the paramount object of the present invention is to provide an improved roller conveyor mount using a stub axle which performs satisfactorily under varying loads and frame misalignments normally experienced in commercial operations.